The standard way to do things is to, onOpen, run a script (Using the onFirstWindowOpen script trigger) that goes to the correct field, finds the data, and then sets the global variable to what you want it to have.

You'd have to save them in a "Prefs" table or something like that. Folks usually make a one-record table with many fields to hold prefs. As the developer you can go into that Prefs table and save data into fields. Then your onOpen script can go to this table, grab the data from the correct field (no find since it is one record) and then store that in a global variable.